1. Field of the Invention
The present invention relates to a shutter device and an image pickup apparatus (image sensing apparatus) using the shutter device.
2. Description of the Related Art
As a shutter device for use in image pickup apparatuses, there is a shutter device in which a group of leading blades and a group of trailing blades are sequentially moved in the same direction, and an exposure operation is performed by use of a slit formed between the two blade groups. In this shutter device, the leading blades, an arm member rotationally connected to the leading blades, and a leading blade driving member for driving the arm member are provided, and the leading blades are driven. Besides, similarly, the trailing blades, an arm member rotationally connected to the trailing blades, and a trailing blade driving member for driving the arm member are provided, and the trailing blades are driven. Incidentally, in the following, operations of the trailing blades will be described mainly.
For example, in a shutter device described in Japanese Patent Laid-open No. 2001-215555 (this shutter device will be referred to also as “the first related art”), when a predetermined setting (cocking) member (referred to also as charging member) is driven by a predetermined driving section, a trailing blade driving member is rotated according to this driving operation. The trailing blade driving member is connected with a spring in the state of being urged in a predetermined direction (a spring charged with elastic energy). The spring is such a spring that the urging force in the predetermined direction can be increased (referred to also as “overcharged”) by deforming it in a certain direction. Specifically, the spring is overcharged when the predetermined setting member is rotationally moved in a predetermined direction.
In addition, with the trailing blade driving member attracted by an electromagnet, after the overcharging, the rotational movement of the trailing blade driving member is restrained. Further, when restraint on the urging force is released by stopping the energization of the electromagnet after the setting member is returned into its original position (after retraction), the trailing blade driving member is driven at high speed by the urging force of the spring. Since the trailing blade driving member is connected with the trailing blades (trailing curtain of shutter) through the arm member, the trailing blades are each moved at high speed from an opening position for a shutter aperture to a closing position for the shutter aperture, according to the driving of the trailing blade driving member. Thus, the trailing blade driving member is turned by the urging force of the spring having been overcharged, and a closing operation of the trailing blades (trailing shutter curtain) is performed according to the turning motion of the trailing blade driving member.
In the shutter device according to the first related art, the spring is overcharged when the trailing blade driving member is turned in a certain direction by the movement of the setting member from a position to another position. In addition, when the trailing blade driving member is turned in the just-mentioned direction (the same direction), the trailing blades are each moved to the opening position for the shutter aperture. In other words, attendant on the turning motion of the trailing blade driving member, an overcharging operation and an opening operation of the trailing blades are carried out simultaneously. Therefore, when the spring is in the overcharged state, the trailing blades are each necessarily present in the opening position, and the trailing blades cannot each be present in the closing position for the shutter aperture when the spring is in the overcharged state.
On the other hand, there is a shutter device different in configuration from the first related art. For example, in a shutter device described in Japanese Patent Laid-open No. Hei 11-95282 (this shutter device will be referred to also as “the second related art”), a driving system for a group of trailing blades includes a trailing blade operating member in addition to a trailing blade driving member.
The trailing blade driving member is connected to an overcharging spring, while the trailing blade operating member is connected to each of the trailing blades through an arm member. In addition, after a setting member rotates the trailing blade driving member to a predetermined position so as to overcharge the spring, the setting member mechanically supports the trailing blade driving member.
Besides, the trailing blade operating member, which is turned coaxially with the trailing blade driving member, can be turned independently of the trailing blade driving member. Specifically, when the trailing blade driving member is turned for an overcharging operation, the trailing blade operating member makes contact with a part of the setting member, whereby the trailing blade operating member is inhibited from rotating. As a result, only the trailing blade driving member is rotated, and the trailing blade operating member is not rotated. Therefore, trailing blades connected to the trailing blade operating member can each continue to be present at the closing position for the shutter aperture. Thus, according to the second related art, the spring can be overcharged while keeping each of the trailing blades in the closing position for the shutter aperture. Besides, in the overcharged state of the spring, mechanical support of the trailing blade driving member by the setting member can also be realized.
Thereafter, energization of an electromagnet is started and attractive holding of the trailing blade driving member by the electromagnet is started, after which the setting member is moved so as to release the contact between the setting member and the trailing blade operating member. In response to this releasing operation, the trailing blade operating member is rotated, whereby the trailing blades are each moved into the opening position for the shutter aperture. In this manner, the trailing blades can each be moved to the opening position for the shutter aperture while maintaining the overcharged state of the spring. It is to be noted here, however, that in this condition, the setting member does not mechanically support the trailing blade driving member.